Suppression of Microsaccades in the Foveola

Article: Brief period of ‘blindness’ is essential to vision
Source: University of Rochester
Published: November 19, 2021
Article: A Brief Period of 'Blindness' Is Key to Us Seeing Fine Details
Source: ScienceAlert
Published: December 5, 2021 

Contrast sensitivity functions in three
spatiotemporal intervals for one observer

Although each of our two eyes possesses a field of vision of 160 degrees, only the most central region of vision, at the foveola where the cones are most densely packed, contains sharp acuity. In order to direct this tiny area of high resolution at a wide range of objects in the visual field, the eyes dart about, often without conscious awareness, in fixational eye movements called saccades. However, these abrupt "sweeps" across the retina also cause a transient blur in vision, which the brain compensates for in the form of saccadic suppression to create a stabilized percept, or a stable view of the world. That is, the brain briefly, so briefly it does not reach conscious awareness, turns off vision as the eyes shift gaze between objects of fixation. Researchers were interested in whether this transient suppression also happens during microsaccades and whether it affects central vision. Senior author of the study explains, "In our lab we have the high-resolution tools to study vision at this small scale, whereas other research has historically focused on the peripheral regions of the eye, where such precision and accuracy are not required." The researchers designed a computer game of dots jumping on a "naturalistic noise-field background" to represent fleas jumping on animal fur, in turn simulating primate grooming behavior. They then recruited eight participants for two sets of experiments and monitored their gaze with eye-tracking. The results showed that suppression occurred immediately before and immediately after the participants shifted gaze. Surprisingly, however, the researchers also found that central vision contrast sensitivity increased after a saccade, so that overall the effect was transiently enhanced. Although the sample size is small, the authors conclude, "These results shed light on the modulations experienced by foveal vision during the saccade-fixation cycle and explain some of the benefits of microsaccades." They will further look into the balance between saccadic suppression and visual enhancement in future work.

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Intoy J, Mostofi N, and Rucci M. "Fast and nonuniform dynamics of perisaccadic vision in the central fovea." PNAS.  118(37):e2101259118. 14 September 2021. https://doi.org/10.1073/pnas.2101259118